In communication electronic apparatuses such as telephones, facsimiles or modems, a portion which is prone to be subjected to electrical shock due to abnormal current (surge current) or abnormal voltage (surge voltage) such as lightning surge or static electricity, including a portion connected to a communication line, a power supply line, an antenna, a CRT driving circuit or the like, is connected with a surge absorber, in order to prevent breaking such as thermal damage or firing of an electronic apparatus or a printed board, on which the electronic apparatus is mounted, due to the abnormal voltage.
Conventionally, for example, a surge absorber using a surge absorbing element having a micro gap has been suggested. This surge absorber is a discharge type surge absorber in which the so-called micro gap is formed in the circumferential surface of a columnar ceramic member covered with a conductive coating film, the surge absorbing element having a pair of cap electrodes located at the both ends of the ceramic member is received in a glass tube together with sealing gas and a sealing electrode having lead wires on the both ends of the cylindrical glass tube is sealed by high-temperature heating.
Recently, in even the discharge type surge absorber, a long life span has been required. As an example of such a surge absorber, there is provided a surge absorber in which, as a covering layer, an SnO2 film having lower volatility upon discharge than that of the cap electrode is formed on a surface where main discharge of the cap electrode is performed. By such a configuration, a metallic component of the cap electrode upon the main discharge is suppressed from being scattered to the inner wall of the glass tube or the micro gap and thus a long life span is realized (for example, see Japanese Unexamined Patent Application Publication No. 10-106712 (page 5 and FIG. 1)).
Further, with miniaturization of the apparatuses, surface mounting is becoming more widespread. As an example of such a surge absorber, there is provided a surface mounting type (metal electrode facebonding (MELF) type) surge absorber in which a lead wire does not exist in a sealing electrode and the sealing electrode is connected and fixed to a board by soldering upon mounting (for example, see Japanese Unexamined Patent Application Publication No. 2000-268934 (FIG. 1)).
As shown in FIG. 30, a surge absorber 300 includes plate-shaped ceramics 153 in which conductive coating films 152 are separately formed on a surface thereof via a discharge gap 151 located at a central portion, a pair of sealing electrodes 155 disposed on the both ends of the plate-shaped ceramics 153, and a barrel-shaped ceramics 157 in which the sealing electrodes 155 are disposed on the both ends thereof and the plate-shaped ceramics 153 is sealed together with sealing gas 156.
Each of the sealing electrodes 155 includes a terminal electrode member 158 and a leaf spring conductor 159 which is electrically connected to the terminal electrode member 158 and is in contact with the conductive coating film 152.
However, with respect to the above-mentioned conventional surge absorber, the following problem exists. That is, in the conventional surge absorber, the SnO2 coating film is, for example, formed by a thin-film forming method such as a chemical vapor deposition (CVD) method. However, since the adhesion of the SnO2 coating film to the cap electrode is weak, the property of the SnO2 coating film cannot be sufficiently accomplished by stripping of the SnO2 coating film.